开云体育

simpleusb output level calculations.  First an explanation.  The simpleusb
channel driver divides the number of mixer steps into 1000 steps. It is a
little more complicated than that depending on log or linear but basically
that is what is done. There has been a long standing bug in the simpleusb
channel driver that causes this to not work properly with genuine CM119B
chips. The divisor assumed 151 mixer steps for ALL chips and when the
CM119B chip is used which only has 37 steps the mapping was totally wrong.
Thus turning the level on the CM119B chips below about 375 actually muted
the chip. No values below that worked. This has now been corrected as the
code reads the number of steps from the chip rather than using a fixed
value and adjusts accordingly.

This change ONLY effects CM119B chips and ONLY the output level - item 3 or
4 on the simpleusb menu. After this update if you are using a CM119B chip
or you hear a difference in the output level (what you hear FROM Allstar)
you should adjust the level accordingly in the simpleusb-tune-menu settings.

There are currently two level methods. Method 0 is logarithmic and is the
default. Method 1 is linear. You can set these methods in the
simpleusb.conf file on a per node basis. The command is:

tx_audio_level_method=0 | 1   ;  0 is the default and is used if this
command does not appear in the config file.

Most users will not need to change the method. Soon there will be an
updated simpleusb-tune-menu program which will allow the setting of these
methods as well as a fine tuning DSP level change in addition to the
current mixer levels. Since the CM119B chip has about 75% less range steps
a finer DSP level will fill in the gaps.

Genuine CM119B chips are now commonly used as no other genuine chip is
being produced. The DMK-URI uses it as does the ARA boards produced by
George other will probably follow as the old stock runs out. Note also the
CM119B chips have less maximum output than the prior varieties. The DMK-URI
board has a 2X op-amp that can be jumpered into the circuit. The ARA rev 2
boards have a fixed 7X rail-to-rail op-amp which gives 5VP-P output into
100 ohms at maximum level.